Subinterval timer drive system

ABSTRACT

A timer drive system including a pair of cam means incrementally and differentially advanceable by a single driven ratchet pawl. The pair of cam means includes ratchet means engageable by the ratchet pawl in a sequence effective for incrementally advancing alternately one cam means and then both cam means so that the cam means are effectively driven at different rates but are maintained synchronized by the common driven ratchet pawl. One of the cam means is operable for effecting subinterval switching.

United States Patent Inventor Gordon Jerry Davh Newton, Iowa June 15, 1970 Sept. 7, 1971 The Maytag Company Newton, Iowa Appl. No. Filed Patented Assignee SUBINTERVAL 'r'nmt DRIVE 12 Chlma,6 Drawing Figs.

us. I 200138 c, 74/567, 260/37 A, zoo/3s B, 200/153 P Int. Cl. 1101b ma, non. 43/10 m0 or semi. 200/6 BA,

21, 27, 33 B, 37 A, 38 B, 38 BA, 38 C, 38 CA, 153 L, 153 LA, 153 LB; 74/122, 125, 567, 569, 577 8; 200/153 P [56] References Cited UNITED STATES PATENTS 2,736,204 2/ 1956 Hill 74/125 2,803,715 8/1957 Guth 200/21 X 2,877,317 3/1959 Euler et al. 200/37 (.1) 3,079,071 2/1963 Staneck 74/125 X 3,234,802 2/1966 Topping et al. 74/567 X 3,170,330 2/1965 Reinecke 200/38 (81 X Primary Examiner-J. R. Scott Attorneys-William G. Landwier and Richard L. Ward ABSTRACT: A timer drive system including a pair of cam means incrementally and differentially advanceable by a single driven ratchet pawl. The pair of cam means includes ratchet means engageable by the ratchet pawl in a sequence effective for incrementally advancing alternately one cam means and then both cam means so that the cam means are effectively driven at different rates but are maintained synchronized by the common driven ratchet pawl. One of the cam means is operable for effecting subinterval switching.

PATENTEUSEP Hen 3503749 Ffgf" SUB INTERVAL SW 5| MOTOR CONTROL SW 50 COMBINED EFFECT flvwewroe 6020a Janey Dav/5 SUBINTERVAL TIMER DRIVE SYSTEM BACKGROUND OF THE INVENTION I. Field of the Invention This invention relates to timer drive systems and more particularly to a self-synchronizing timer drive system.

2. Description of the Prior Art Timers have been shown in prior art patents that include a switch periodically operated between open and closed positions during each interval of advance of the sequence control cam means. These timers are sometimes referred to as subinterval timers. The subinterval switching has been effected by a continuously rotatable cam driven in some timers, by the same motor that operates the step-by-step incremental advance of the sequence control cam means. In these prior art constructions, however, synchronization of the switching controlled by the subinterval cam means and the switching controlled by the sequence control cam means was troublesome to obtain because of manufacturing tolerances making it difficult to accurately locate the subinterval switch relative to the subinterval cam means and to accurately locate the step-by-step mechanism relative to the sequence control cam means. In subinterval timers it is desirable, if not essential, to insure that the make and break of the subinterval and sequence control switches are accurately synchronized. Prior art has been unable to achieve such accurate synchronization.

SUMMARY OF THE INVENTION It is an object of the instant invention to provide a selfsynchronizing timer drive mechanism.

It is a further object of the instant invention to provide an incrementally advanceable timer wherein subinterval switching cam means is maintained accurately synchronized with sequence control cam means through a common advancing member.

It is a further object of the instant invention to provide, in a timer having subinterval switching, a drive system that is operable for maintaining synchronization of the sequence control cam means to the subinterval switching cam means during each advance of the sequence control cam means.

It is a still further object of the instant invention to provide a combination timer cam and drive wheel construction responsive to common ratchet means for achieving synchronization of operation of the sequence control switches and a subinterval switch.

The instant invention achieves these objects in a timer mechanism having first and second drive wheels operable for driving a subinterval switching cam and a sequence control cam, respectively, and advanceable by a common drive element that advances one drive wheel and then periodically advances both drive wheels to differentially advance the cams while maintaining accurate synchronization therebetween.

Operation of the device and further objects and advantages thereof will become evident as the description proceeds and from an examination of the accompanying sheet of drawings.

BRIEF DESCRIPTION OF THE DRAWINGS The drawings illustrate a preferred embodiment of the invention with similar numerals referring to similar parts throughout the several views wherein:

FIG. 1 show an overall view of a timer mechanism embodying the instant invention;

FIG. 2 shows a sectional view of the sequence control cam means and subinterval switching cam means as taken substantially along line 2-2 of FIG. 4;

FIG. 3 shows a sectional view of the sequence control cam means and subinterval switching cam means as taken substantially along line 3--3 of FIG. 4;

FIG. 4 shows an enlarged fragmentary view of the ratchet teeth of the pair of cam means and the ratchet pawl engageable therewith;

FIG. 5 shows a simple electrical schematic illustrating one use of the preferred embodiment of the instant invention; and

FIG. 6 shows a fragmentary portion of the profile of the sequence control cam and subinterval switching cam showing the sequential operation of the switches of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there is shown a timer mechanism 10 generally defined by the housing 11 to which is mounted a drive means 13. A fragmentary portion of the housing 11 has been removed to expose the sequence control means 14 comprising, in this embodiment, a molded disclike assembly 15 having cam tracks 16 on at least one face. The disclike assembly I5 is mounted on a shaft 19 for rotation within the housing 11. The cam tracks 16 are operable for actuating a plurality of switches (not shown) that are electrically connected to the terminals 20 that are in turn connectable to the electrical circuit of the controlled appliance.

Referring briefly to FIGS. 2 and 3, it is seen that the disclilte assembly 15 in this embodiment includes a first disclike member 23 mounted on the shaft 19 and having cam means or cam tracks 16 on one face and also includes a second annular or ringlike member 24 having a cam track 25 on its face. As best shown in FIGS. 1 and 4, and as will be more fully discussed hereinafter, these rotatable members include drive wheel means 26 and 27, respectively, in the form of ratchet v teeth on the periphery.

These two rotatable members 23 and 24 form part of the sequence control means 14 and for the purposes of this description will be designated as the sequence control cam means 23 and the subinterval switching cam means 24. It is to be understood that these designations include the cam tracks 16 and 25 and the ratchet wheels 26 and 27 associated with the rotatable members 23 and 24, respectively. In other words, the term sequence control cam means" 23 includes the sequence control cam track 16 on the face of the disclike member and the ratchet wheel 26 on the periphery thereof.

The drive means 13 includes an electrically energizable motor 30 attached to the housing 11 for advancing the sequence control cam means 23 and the subinterval switching cam means 24. The drive means 13 further includes a ratchet lever 31 and pawl 32. The pawl 32 is pivotally mounted on the lever 31 with the ratchet lever 31 being in turn pivotally mounted on the housing 11 by pivot pin 33 and driven by the motor 30 against a spring 34 through a cam or eccentric driver 35 for effectively storing energy in the ratchet spring 34 as the ratchet lever 31 is pivoted is a clockwise direction about the pivot pin 33. The small spring 36 biases the pawl32 into driving engagement with the ratchet teeth but also permits the pawl to ride up over each tooth as the lever 31 is pivoted in a clockwise direction. At periodic intervals, the ratchet lever 31 is released by the cam or eccentric driver 35 to permit rapid, high torque, movement of the ratchet pawl 32 in a counterclockwise direction relative to the pivot pin 33 to advance the subinterval switching cam means 24 or the subinterval switching cam means 24 and the sequence control cam means 23 in a clockwise direction about the axis of shaft 19 by means to be described hereinafter. A biased antibackup means 39 prevents the sequence control cam means 23 and subinterval switching cam means 24 from moving in the counterclockwise direction.

The timer mechanism 10, including the housing, the switching, and the motor driven ratchet advancing system, as far as has been explained to this point, is similar to the sequence control mechanism shown in US. Pat. 3,053,947. Other conventional timer systems, however, could be used with the instant invention in its broadest aspects as will be discussed hereinafter.

As has been previously indicated, the instant invention is directed to providing subinterval switching and timing in an appliance sequence control means. Subinterval switching and timing is essential in some appliances since certain components or circuits need to be operated for only a few seconds,

such duration being less than the duration of each increment of the sequence control cam which has a time period of 30 or 60 seconds, for example.

Referring again to FIGS. 2 and 3, the sequence control cam means 23 includes a plurality of sequencing or program control cam tracks 16 on one face thereof for controlling the cycle of the appliance. The ringlike subinterval switching cam means 24 is movably mounted on a shoulder 40 formed near the outer periphery of the sequence control cam means 23 and includes a cam track 25 on its face for controlling the subinterval switching. The ratchet wheels 26 and 27 on the outer periphery of the cam means 23 and 24 comprise a series of ratchet teeth engageable by the ratchet pawl 32 which is shown in phantom lines in FIGS. 2 and 3.

Referring to FIG. 4, it is noted that the ratchet teeth of both ratchet wheels 26 and 27 are evenly spaced around the periphery. In the preferred embodiment, each ratchet wheel includes 60 teeth having a 6 spacing. It is noted, however, that the outside diameter of the ratchet teeth 27 on the subinterval switching cam means is greater than the outside diameter of the ratchet teeth 26 of the sequence control cam means. Also, the root diameter between alternating pairs of teeth of the subinterval switching cam ratchet wheel 27, such as between the pair of teeth 41 and 42, extend inwardly to correspond with the root diameter between each pair of teeth on the sequence control cam ratchet wheel 26. Between the other alternating pairs of teeth of the subinterval switching cam ratchet wheel 27, such as between the pair of teeth 42 and 43, the root diameter of the subinterval switching ratchet wheel 27 is just outside the outer diameter of the teeth on the sequence control cam ratchet wheel 26. The subinterval switching ratchet wheel 27 includes what may be called deep teeth and shallow teeth alternating around the periphery.

The ratchet pawl 32 is sufficiently wide, as shown in FIGS. 2 and 3, and is positioned to engage both ratchet wheels 26 and 27 at the same time. It is therefore seen that as the ratchet pawl 32 is cyclically drawn in a counterclockwise direction relative to the ratchet wheels 26 and 27, as shown in FIG. 4, the pawl 32 is operable for engaging with one of the shallow teeth and advancing only the subinterval switching cam means 24 and then during alternate steps is operable for engaging one of the deep teeth and simultaneously advancing both cam means 23 and 24 one increment. It will thus be seen that the intermediate or subinterval advancement of the subinterval switching cam means 24 is operable for effecting actuation of subinterval switches independently of the sequencing control cam means 23 and for shorter time intervals than is otherwise possible. The pawl 32 will eventually engage each of the teeth of the sequence control ratchet wheel 26 for advancing the sequence control cam means 23 through a full cycle of operations.

The antibackup means 39 is constructed to include a pair of separately operable and separately biased fingers individually engageable with the two ratchet wheels 26 and 27 to prevent backup of the cam means 23 and 24.

The subinterval switching ratchet wheel 27 may include, in alternate embodiments, two or three shallow teeth between each of the deep teeth to provide additional arid/or shorter duration subinterval switching. The sequence control means could also, for example, be in the form of a cam stack having the cam profiles around the periphery of individual cam members mounted on a shaft which is in turn driven by a ratchet wheel similarly mounted on the shaft. The subinterval switching cam means could similarly be in the form of a separate cam and ratchet wheel combination constructed and disposed so that the two ratchet wheels are adjacently positioned for engagement by the ratchet pawl.

A specific use of the subinterval switching is shown in FIGS. and 6. FIG. 5 shows a fragmentary portion of an electrical circuit and includes a line switch 49 in series with a pair of parallel-connected timer-controlled switches 5t) and Sll and in further series with an appliance drive motor 53, for example. One of the timer control switches shown in FIG. 5 is controlled by a sequence control cam track 16 and may be considered the motor control cam 50 while the other switch may be considered a subinterval switch 5 controlled by the subinterval switching cam track 25. It is not uncommon in appliances to reverse the direction of the motor 53 and necessitating the provision of an interval on the main timer cam track 16 to allow the motor 53 to come to a stop before energizing it in the reverse direction. In a timer having no subinterval switching, this rest period requires a full time interval and thus uses more time than is necessary to accomplish the reversing procedure.

Referring to FIG. 6, a fragmentary portion of a cam profile chart shows an interval, set off by lines 54 and 55, for effecting motor reversal. In FIG. 6 the shaded areas indicate the switch is closed. The subinterval switching cam track 25 effects an opening of the subinterval switch 51 during the initial portion of the interval and a closing of the subinterval switch 51 during the terminal portion of the interval. During the interval set off by lines 54 and 55, the cam chart shows the motor control switch 50 is open. The combined effect of the parallel connected switches is shown by the third line in FIG. 6 whereby the motor 53 is deenergized for the first portion of the interval and then is energized through the subinterval switch 51 during the last portion of the interval. The pause or period of interruption of the motor 53 is effectively reduced to one-half of the interval. This subinterval switching procedure becomes especially important in the appliances in which a great deal of switching is required to accomplish a complete cycle of operation.

One of the primary problems of subinterval switching arrangements in previous timer mechanisms has been that of achieving synchronization between the sequence control switching with the subinterval switching. For example, it is essential that the motor control switch 50 be closed before the opening of the subinterval switch 51 at the vertical line 55 if proper motor energization is to be assured. In the instant invention, synchronization between the two switches is accurately maintained through the common advancement of the cam means by a single ratchet pawl. Each time the ratchet pawl 32 engages one of the deep teeth of the subinterval switching ratchet wheel, it engages also the ratchet teeth of the sequence control ratchet wheel to achieve this accurate synchronization. The synchronization between the cam tracks is thus assured during each advance of the sequence control cam means.

It is therefore seen that the instant invention provides an improved subinterval timer drive system in which synchronization is achieved without the precise assembly and adjustment requirements of prior art devices. The self-synchronizing feature of the instant invention is absent from other prior art subinterval switch timer drive systems.

In the foregoing drawings and specification, there has been set forth a preferred embodiment of the invention and, although specific terms are employed, these are used in a generic and descriptive sense only and not for purposes of limitation. Changes in form and the proportion of parts as well as the substitution of equivalents are contemplated as circumstances may suggest or render expedient without departing from the spirit or scope of this invention as defined in the following claims.

lclaim:

ll. A subinterval timer, the combination comprising: a housing; sequence control means including sequence control cam means and subinterval switching cam means movably supported in said housing relatively movable to each other and further including a plurality of switches actuated by said sequence control cam means and said subinterval switching cam means; and drive means for advancing said sequence control cam means and said subinterval switching cam means through a predetermined cycle of operation, said drive means including advancing means drivingly engageable with said subinterval switching cam means and periodically engageable with both said sequence control cam means and said subinterval switching cam means for efiecting advancement of said subinterval switching cam means after a predetermined period of time and efiecting advancement of both said sequence control cam means and said subinterval switching cam means after a multiple of said predetermined period of time whereby said subinterval switching cam means and said sequence control cam means are advanced at different effective rates while maintained in synchronization.

2. A timer, the combination comprising: a housing; sequence control means including first and second relatively movable cam means supported in said housing and further including first and second switches operated by said first and second cam means; drive means including incremental advancing means operable for advancing said first and second cam means; first means drivingly connected to said first cam means and engageable by said advancing means; and second means drivingly connected to said second cam means and periodically engageable by said advancing means, said first means being normally engageable by said advancing means for regular predetermined incremental advancement of said first cam means and formed to effect common engagement of said advancing means with said first means and said second means after at least one predetermined intermediate advancement of said first cam means alone for advancing said first and second cam means substantially simultaneously whereby said first and second cam means are advanced at different effective rates while synchronization is maintained therebetween.

3. A timer, the combination comprising: a housing; sequence control means including relatively movable sequence control cam means and subinterval switching cam means supported within said housing and operable for actuating first and second switches; a driven ratchet pawl means operable for advancing said sequence control cam means and said subinterval switching cam means; first ratchet means drivingly connected to and comprising a portion of said subinterval switching cam means engageable by said ratchet pawl means; and second ratchet means drivingly connected to and comprising a portion of said sequence control cam means and periodically engageable by said ratchet pawl means, said first ratchet means being normally engageable by said ratchet pawl means for regular predetermined incremental advancement of said subinterval switching cam means and formed to effect common engagement of said ratchet pawl means with said first ratchet means and said second ratchet means after a predetermined number of intermediate incremental advancements of said subinterval switching earn means alone for advancing said sequence control cam means and subinterval switching cam means substantially simultaneously whereby said sequence control cam means and subinterval switching cam means are advanced at different efiective rates while synchronization is maintained therebetween.

4. in a timer as defined in claim 3 wherein one of said sequence control cam means and said subinterval switching cam means is in the form of a disclike member and wherein said first ratchet means is in the form of first ratchet teeth on the periphery thereof for engagement by said ratchet pawl means.

5. In a timer as defined in claim 4i wherein the other of said sequence control cam means and said subinterval switching cam means is in the form of an annular member rotatably mounted on said one of the sequence control cam means and the subinterval switching cam means and includes second ratchet teeth on the periphery thereof juxtaposed to said first ratchet teeth.

6. In a timer as defined in claim 3 wherein said first ratchet means includes regularly spaced teeth extending beyond said second ratchet means for regular engagement and advancement by said driven ratchet pawl means and further includes recesses between predetermined numbers of teeth for permitting engagement of said ratchet pawl means with said second ratchet means while engaging said first ratchet means and thereby effecting substantially simultaneous advancement of said sequence control cam means and said subinterval tqli nssa nmsea an i mm.

7. In a timer as defined in claim 3 wherein said first and second ratchet means includes a plurality of ratchet teeth operatively engageable by said ratchet pawl means and wherein the radial depth of a first portion of the ratchet teeth of said first ratchet means permits common engagement of said ratchet pawl means with said first and second ratchet means and the radial depth of a second portion of the ratchet teeth of said first ratchet means prevents engagement of said ratchet pawl means with said second ratchet means.

8. A timer, the combination comprising: a housing; sequence control means including first and second rotatable members supported within said housing and operable for actuating first and second switches, said first rotatable member including cam means on at least one face thereof and further including first ratchet teeth around the periphery thereof, said second rotatable member being rotatable relative to said first rotatable member and including cam means on one face thereof and second ratchet teeth around the periphery thereof closely juxtaposed to said first ratchet teeth; and driven ratchet pawl means for common engagement with said first and second ratchet and advancement thereof, said first ratchet teeth extending beyond said second ratchet teeth and including shallow intermediate teeth operatively engageable with said ratchet pawl means while preventing operative engagement of said ratchet pawl means with the second ratchet teeth for achieving subinterval advancement of said first rotatable member.

9. A timer as defined in claim 8 wherein each of said rotatable members includes the same number of teeth on the periphery thereof and wherein said first rotatable member includes alternating full depth and shallow depth teeth whereby said first rotatable member is advanced twice for each advance of said second rotatable member with one of the advanced of the first rotatable member being synchronized with the advance of said second rotatable member.

10. A timer, the combination comprising: a housing; sequence control means including subinterval switching cam means having a first cam track on a face thereof and a first ratchet wheel on the periphery thereof and further including sequence control cam means rotatable relative to said subinterval switching cam means and having a second cam track on a face thereof and a second ratchet wheel on the periphery thereof juxtaposed to the first ratchet wheel of said subinterval switching cam means; and a driven ratchet pawl means operable for advancing said subinterval switching cam means and said sequence control cam means, said first ratchet wheel extending radially beyond said second ratchet wheel to normally engage with said ratchet pawl means and selectively prevent engagement of said ratchet pawl means with the second ratchet wheel, said first ratchet wheel being formed with recesses between selected groups of ratchet teeth extending radially inwardly to generally the second ratchet wheel of said sequence control cam means to receive said ratchet pawl means and to periodically effect generally simultaneous driving engagement of said ratchet pawl means with said first and second ratchet wheels.

11. A timer as defined in claim 10 wherein one of said subinterval switching cam means and said sequence control means is formed as a disclike member having a cam track on one face thereof and ratchet teeth formed on the periphery thereof and wherein the other of said subinterval switching cam means and said sequence control cam means is an annular ring mounted on said disclike member and formed with a cam track on one face thereof and ratchet teeth on the periphery thereof and positioned juxtaposed to the ratchet teeth on the disclike member for common engagement by said ratchet pawl.

If, A timer as dfiheiiii 615E ii, wherein the ratchet teeth on said subinterval switching cam means and said sequence control cam means are similarly formed and the ratchet teeth on said subinterval switching cam means include shallow intermediate teeth for periodically preventing operative engagement of the ratchet pawl with the ratchet teeth of said sequence control cam means whereby the subinterval switching cam means is advancealfe on a self-synchronizing subinterval basis relative to advancement of said sequence control cam means. 

1. A subinterval timer, the combination comprising: a housing; sequence control means including sequence control cam means and subinterval switching cam means movably supported in said housing relatively movable to each other and further including a plurality of switches actuated by said sequence control cam means and said subinterval switching cam means; and drive means for advancing said sequence control cam means and said subinterval switching cam means through a predetermined cycle of operation, said drive means including advancing means drivingly engageable with said subinterval switching cam means and periodically engageable with both said sequence control cam means and said subinterval switching cam means for effecting advancement of said subinterval switching cam means after a predetermined period of time and effecting advancement of both said sequence control cam means and said subinterval switching cam means after a multiple of said predetermined period of time whereby said subinterval switching cam means and said sequence control cam means are advanced at different effective rates while maintained in synchronization.
 2. A timer, the combination comprising: a housing; sequence control means including first and second relatively movable cam means supported in said housing and further including first and second switches operated by said first and second cam means; drive means including incremental advancing means operable for advancing said first and second cam means; first means drivingly connected to said first cam means and engageable by said advancing means; and second means drivingly connected to said second cam means and periodically engageable by said advancing means, said first means being normally engageable by said advancing means for regular predetermined incremental advancement of said first cam means and formed to effect common engagement of said advancing means with said first means and said second means after at least one predetermined intermediate advancement of said first cam means alone for advancing said first and second cam means substantially simultaneously whereby said first and second cam means are advanced at different effective rates while synchronization is maintained therebetween.
 3. A timer, the combination comprising: a housing; sequence control means including relatively movable sequence control cam means and subinterval switching cam means supported within said housing and operable for actuating first and second switches; a driven ratchet pawl means operable for advancing said sequence control cam means and said subinterval switching cam means; first ratchet means drivingly connected to and comprising a portion of said subinterval switching cam means engageable by said ratchet pawl means; and second ratchet means drivingly connected to and comprising a portion of said sequence control cam means and periodically engageable by said ratchet pawl means, said first ratchet means being normally engageable by said ratchet pawl means for regular predetermined incremental advancement of said subinterval switching cam means and formed to effect common engagement of said ratchet pawl means with said first ratchet means and said second ratchet means after a predetermined number of intermediate incremental Advancements of said subinterval switching cam means alone for advancing said sequence control cam means and subinterval switching cam means substantially simultaneously whereby said sequence control cam means and subinterval switching cam means are advanced at different effective rates while synchronization is maintained therebetween.
 4. In a timer as defined in claim 3 wherein one of said sequence control cam means and said subinterval switching cam means is in the form of a disclike member and wherein said first ratchet means is in the form of first ratchet teeth on the periphery thereof for engagement by said ratchet pawl means.
 5. In a timer as defined in claim 4 wherein the other of said sequence control cam means and said subinterval switching cam means is in the form of an annular member rotatably mounted on said one of the sequence control cam means and the subinterval switching cam means and includes second ratchet teeth on the periphery thereof juxtaposed to said first ratchet teeth.
 6. In a timer as defined in claim 3 wherein said first ratchet means includes regularly spaced teeth extending beyond said second ratchet means for regular engagement and advancement by said driven ratchet pawl means and further includes recesses between predetermined numbers of teeth for permitting engagement of said ratchet pawl means with said second ratchet means while engaging said first ratchet means and thereby effecting substantially simultaneous advancement of said sequence control cam means and said subinterval switching cam means.
 7. In a timer as defined in claim 3 wherein said first and second ratchet means includes a plurality of ratchet teeth operatively engageable by said ratchet pawl means and wherein the radial depth of a first portion of the ratchet teeth of said first ratchet means permits common engagement of said ratchet pawl means with said first and second ratchet means and the radial depth of a second portion of the ratchet teeth of said first ratchet means prevents engagement of said ratchet pawl means with said second ratchet means.
 8. A timer, the combination comprising: a housing; sequence control means including first and second rotatable members supported within said housing and operable for actuating first and second switches, said first rotatable member including cam means on at least one face thereof and further including first ratchet teeth around the periphery thereof, said second rotatable member being rotatable relative to said first rotatable member and including cam means on one face thereof and second ratchet teeth around the periphery thereof closely juxtaposed to said first ratchet teeth; and driven ratchet pawl means for common engagement with said first and second ratchet and advancement thereof, said first ratchet teeth extending beyond said second ratchet teeth and including shallow intermediate teeth operatively engageable with said ratchet pawl means while preventing operative engagement of said ratchet pawl means with the second ratchet teeth for achieving subinterval advancement of said first rotatable member.
 9. A timer as defined in claim 8 wherein each of said rotatable members includes the same number of teeth on the periphery thereof and wherein said first rotatable member includes alternating full depth and shallow depth teeth whereby said first rotatable member is advanced twice for each advance of said second rotatable member with one of the advanced of the first rotatable member being synchronized with the advance of said second rotatable member.
 10. A timer, the combination comprising: a housing; sequence control means including subinterval switching cam means having a first cam track on a face thereof and a first ratchet wheel on the periphery thereof and further including sequence control cam means rotatable relative to said subinterval switching cam means and having a second cam track on a face thereof and a second ratchet wheel on the periphery thereof juxtaposed to the first ratchet wheel of said subintervAl switching cam means; and a driven ratchet pawl means operable for advancing said subinterval switching cam means and said sequence control cam means, said first ratchet wheel extending radially beyond said second ratchet wheel to normally engage with said ratchet pawl means and selectively prevent engagement of said ratchet pawl means with the second ratchet wheel, said first ratchet wheel being formed with recesses between selected groups of ratchet teeth extending radially inwardly to generally the second ratchet wheel of said sequence control cam means to receive said ratchet pawl means and to periodically effect generally simultaneous driving engagement of said ratchet pawl means with said first and second ratchet wheels.
 11. A timer as defined in claim 10 wherein one of said subinterval switching cam means and said sequence control means is formed as a disclike member having a cam track on one face thereof and ratchet teeth formed on the periphery thereof and wherein the other of said subinterval switching cam means and said sequence control cam means is an annular ring mounted on said disclike member and formed with a cam track on one face thereof and ratchet teeth on the periphery thereof and positioned juxtaposed to the ratchet teeth on the disclike member for common engagement by said ratchet pawl.
 12. A timer as defined in claim 11, wherein the ratchet teeth on said subinterval switching cam means and said sequence control cam means are similarly formed and the ratchet teeth on said subinterval switching cam means include shallow intermediate teeth for periodically preventing operative engagement of the ratchet pawl with the ratchet teeth of said sequence control cam means whereby the subinterval switching cam means is advanceable on a self-synchronizing subinterval basis relative to advancement of said sequence control cam means. 